The invention relates to a process for determining the composition of aqueous solutions of NH.sub.3 and CO.sub.2 from which ammonium carbamate or ammonium carbonate.H.sub.2 O (ammonium carbonate with one water of crystallization) crystallizes out upon cooling to below the saturation temperature. In the following discussion, reference will be made only to ammonium carbamate, which term should be understood to include also ammonium carbonate.
Such solutions occur in practice as process streams in, for example, the preparation of urea and/or the preparation of melamine. In the preparation of urea, to obtain optimum conversion in the synthesis zone it is necessary that the water content of carbamate solutions to be recirculated to this zone should be kept as low as possible while still preventing carbamate from crystallizing out. To achieve this objective, the composition of such a process stream must be know. Thus far, various methods of analysis have been used to analyze such solutions. However, these methods have been difficult to apply in that the method of analysis used is too slow to permit timely corrective measures in the event of deviations from the correct composition. The object of the present invention is to provide a process for determining the composition of such solutions in which process the aforementioned difficulties are overcome.